PHILADELPHIA — An engineer jammed on the emergency brakes just seconds before Tuesday’s fatal Amtrak derailment, but the train — traveling at 106 miles an hour, more than twice the speed limit — slowed only slightly, federal authorities said, before hurtling off its tracks, killing at least seven people and injuring more than 200.

Survivors who emerged battered and bloodied described a chaotic scene, with passengers thrown against walls, furniture and one another, and luggage and other items and falling on terrified riders. By Wednesday night, as cars were being removed, some passengers still had not been accounted for.

Investigators say that it is too early to know whether speed alone caused the wreck and that they will examine other factors, such as track conditions, throttle and brake settings and alarms in the engineer’s cab. They were also studying video from a camera mounted on the locomotive, and they plan to interview the engineer, who spoke to the police but may have given only limited information, Mayor Michael A. Nutter said.

“As we know, it takes a long time to decelerate a train,” said Robert Sumwalt, the National Transportation Safety Board official who is leading the investigation, in a news conference. He added, “You’re supposed to enter the curve at 50 miles per hour. He was already in the curve.”

The crash occurred on a stretch of the Northeast Corridor — the Washington-to-Boston route — that did not have a signal system known as positive train control, which can dictate speeds and slow trains around curves.

Mr. Sumwalt said positive train control could have prevented the crash. “Based on what we know right now,” he told reporters at a news conference here, “we feel that had such a system been installed on this section of track, this accident would not have occurred.”

Even without the system, rail safety experts said Amtrak locomotives have multiple systems to alert train operators to excess speed, with warning lights and sound alarms. Mr. Sumwalt said he did not know yet whether those systems had worked.

The train — Northeast Regional Train No. 188, from Washington to New York — was carrying 238 passengers and a five-member crew when it jumped the tracks shortly before 9:30 p.m. Tuesday while coming up on a sharp left turn at a spot not far from the site of a 1943 derailment that killed 79 people. The crash shut down train service between New York and Philadelphia, creating delays for business travelers and commuters, and immediately set off a debate in Washington about the nation’s rail infrastructure — on the same day that the House Appropriations Committee rejected a funding increase for Amtrak.

Survivors — including a former congressman, Patrick Murphy — described terrifying moments in which the train seemed to soar through the air before the locomotive and cars landed in a twisted, mangled, pretzel-like mess. Passengers said they saw blood and bodies everywhere as they struggled to escape.

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The United States Naval Academy’s superintendent said Thursday that Justin Zemser, the midshipman who died in an Amtrak train derailment, was a talented and highly respected young man.Published OnMay 14, 2015CreditCreditU.S. Naval Academy, via Associated Press

Some called 911; a pregnant woman pulled up the GPS on her phone to direct rescue personnel to the scene. Carol Cissel, a Unitarian minister from Somerset, N.J., who had been visiting her grandson in Maryland, said she was near the front of the train’s quiet car, in an aisle seat, when the train tilted right and kept tipping — and screams started to ring out.

“The car, it was like being in the dryer, it rolled over,” she said Wednesday, after being treated for a concussion and bumps and bruises, including one on the back of her head. She landed near a pregnant woman, who looked at her, frightened and holding her stomach. There was an open window high above them.

“I pushed the pregnant woman up in front of me and out of the hole,” Ms. Cissel said. “Nobody was getting out of there by themselves.”

As emergency workers picked through the rubble Wednesday night, Mr. Nutter said another 25 police officers and supervisors had gone out to search the area again. In addition to the dead, at least eight people were critically injured.

“They’ve widened the search area given the horrific nature of what happened there,” Mr. Nutter said. “The prospect of some passengers possibly being ejected from the train is real.”

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Rescue workers at the wreckage of the Amtrak train, which crashed while traveling more than twice the speed limit.CreditJoseph Kaczmarek/Associated Press

As the search for survivors — or perhaps more victims — continued, the names of the dead began to trickle out. They included Justin Zemser, 20, a midshipman at the United States Naval Academy; Jim Gaines, 48, a video software architect from Plainsboro, N.J., who worked for The Associated Press; Rachel Jacobs, the chief executive of ApprenNet, an education technology company in Philadelphia; Abid Gilani, a senior vice president of Wells Fargo; and Derrick Griffith, a dean at Medgar Evers College.

The suspension of train service between New York and Philadelphia disrupted travel from Washington to Boston. As travelers scrambled to find alternative routes, buses filled up and airline shuttles were booked.

The crash also raised questions for lawmakers — including Senator Patrick J. Toomey, Republican of Pennsylvania, who said he travels Amtrak’s Northeast Corridor all the time, frequently on Train No. 188 — about what kinds of policy changes might be necessary. But Mr. Toomey and his fellow Pennsylvania senator, Bob Casey, a Democrat, both declined to discuss what steps Congress might take, though Mr. Casey said he has long argued for more funding for Amtrak.

Tuesday’s wreck occurred as the New York-bound train passed through a rail yard called Frankford Junction northeast of Center City Philadelphia where multiple freight and passenger routes converge and Amtrak’s Northeast Corridor makes one of its sharpest turns.

Although the maximum allowed speed on the curve is 50 m.p.h., data downloaded from the “black box” recorder showed that just before it crashed, the train was speeding at 106 m.p.h., Mr. Sumwalt said. He said the speed limit on the straightaway leading to the curve was 80 m.p.h.; the Federal Railroad Administration said it was 70.

“Just moments before the derailment,” Mr. Sumwalt said, “the engineer applied full emergency brake application.” When the data recorder stopped working three seconds later, he said, the speed was 102 m.p.h.

The engineer’s name was not released, but Philadelphia news organizations, citing law enforcement officials, identified him as Brandon Bostian of Queens, N.Y.

In an interview that aired Thursday on the ABC News program “Nightline,” Robert Goggin, who was identified on the program as Mr. Bostian’s lawyer, said the engineer had injuries that required 14 stitches in his head and some staples in one leg. He added that the engineer gave police officers his cellphone number and a sample of his blood.

“He has absolutely no recollection of the incident or anything unusual,” Mr. Goggin said on “Nightline.” “The next thing he recalls is being thrown around, coming to, finding his cellphone and dialing 911.”

Officials said the data recorder, found early Wednesday, was taken first to Amtrak’s operations center in Delaware, and then to the safety board’s laboratory in Washington.

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The Philadelphia mayor, the Amtrak chairman and a member of the National Transportation Safety Board discussed the investigation into Tuesday night’s train derailment.Published OnMay 13, 2015CreditCreditMatt Slocum/Associated Press

Russ Quimby, a retired rail crash investigator with the safety board, said: “When you are depending entirely on a human being, the engineer in this case, then there is an opening for a human error and a tragedy like this one. If you have no system to regulate the speed, then that’s the core failure.”

Dozens of passengers were sent to area hospitals. Temple University Hospital in Philadelphia received 54 patients, including one who died overnight from a massive chest injury, said Dr. Herbert E. Cushing, the chief medical officer. They included people from Spain, Belgium, Germany, Albania and India.

“I think we’re fortunate that there weren’t more deaths,” he said. Dr. Cushing said that most of the patients suffered rib fractures from being thrown around the train. Several also had other broken bones, he said, and some had punctured lungs, but relatively few had head injuries. Most were treated at the hospital and released.

On Wednesday, after touring the crumpled wreckage, Mayor Nutter said he was astonished that anyone had survived.

“To see these cars, these huge metal vehicles turned upside down, one almost split in half, the engine almost completely separated — you know that this is a devastating situation,” Mr. Nutter said. He added, “It’s amazing; it’s incredible that so many people walked away.”

Correction:

An earlier version of this article misstated, at one point, the day on which the train derailment occurred. It was on Tuesday, not Wednesday.